Spool filled with multiple elongated elements wound closely together

ABSTRACT

A spool ( 10 ) filled with two or more elongated elements ( 14, 16 ) such as steel cords wound in parallel and in several windings upon the spool is provided. The distance s between two neighboring elongated elements, as measured along a line parallel to the axis ( 18 ) of the spool ( 10 ), is not more than 10 mm along 90% of the length of each elongated element. The advantage is that unwinding problems such as sags and downstream processability problems are avoided.

FIELD OF THE INVENTION

The present invention relates to a spool filled with two or moreelongated elements wound in parallel and in several windings upon thespool. The present invention also relates to a method of providing sucha spool. The terms ‘elongated elements’ refer to elements thelongitudinal dimension of which is more than hundred times larger thanthe cross-sectional dimensions. Common examples of elongated elementsare round or flat steel wires, steel cords, textile yarns, copperstrands, . . .

BACKGROUND OF THE INVENTION

Assemblies and apparatus for winding a plurality of elongated elementssuch as wires, cables or cords on one single spool are known in the art.

As a matter of example, when manufacturing composites of rubber withsteel cord, such as tires, the steel cords are very often drawn from acreel, which comprises a large number of spools, e.g. 20 to 150 spoolsin some embodiments and e.g. 500 to 1000 spools in other embodiments.The great number of steel cords is then guided in parallel in order tobe inserted between two layers of rubber. A drawback of such a system isthat it takes a lot of time to replace the empty spools by filledspools. Using spools with multiple winding, i.e. where a plurality ofsteel cords is wound upon one spool, reduces the number of spools in acreel and increases the flexibility of the use of such a creel.

However, the simultaneous unwinding of a plurality of elongated elementsfrom such a single spool, may cause difficulties and the subsequentparallel processing of the plurality of elongated elements may lead toan unacceptable degree of fractures and processability problems.

The unwinding difficulties and the processability problems and fracturesduring the subsequent treatment may be due to a variation in diameter ofthe elongated elements during their winding, or may be due to the factthat elongated elements become entangled during their winding, or may bedue to the fact that the elongated elements, although wound at the sametime on the same spool, take different lengths on the spool. Otherdifficulties during the unwinding operations are due to differenttensions in the individual elongated elements during the windingoperation.

GB-B-1 163 983 discloses a method for winding a plurality of elongatedelements on one single spool whereby it is aimed at keeping the windinglengths of the elongated elements substantially equal to each otherdespite some variations in diameter of the elongated element. Thesolution used to obtain substantially the same lengths is to increasethe tension in elongated elements with an increased diameter in order toreduce the winding diameter and to decrease the tension in elongatedelements with a decreased diameter in order to increase the windingdiameter. A separation comb is mounted upstream the winding spool inorder to avoid disentanglement of the neighboring elongated elements.

EP-A-0 780 333 discloses an assembly for winding multiple elongatedelements on a spool, where the tensions in the elongated elements arekept substantially constant and equal. In order to obtain constant andequal tensions, the assembly comprises following parts:

-   -   a set of independently driveable capstans, one for each        individual elongated element to be wound;    -   a single spool where the plurality of elongated elements are to        be wound;    -   first monitoring means for measuring the tensions of each        individual elongated element of a subgroup of the plurality of        elongated elements;    -   first control means for steering individually the revolution        speed of the capstans driving the elongated elements of the        subgroup such that said tensions remain substantially constant        and substantially equal to each other.

Before their winding on the spool, a comb is used to prevent the wiresfrom entangling with each other and from jumping over each other.

So the prior art has provided solutions both for keeping the lengthsequal and the tensions constant in the elongated elements to be wound.

Despite these solutions problems are still experienced in determinedcircumstances when unwinding the plurality of elongated elements at thesame time. More particularly, when unwinding, some of the elongatedelements show unacceptable large sags. These sags may lead toentanglement with the neighboring elements or to wear or pollution ofthe sagged elements when these elements drag over the floor of theunwinding shop. Still another problem is that the ultimate product, e.g.a rubber strip with the elongated elements may show some unacceptablewrinkles.

SUMMARY OF THE INVENTION

It is an object of the present invention to avoid the drawbacks of theprior art.

It is another object of the present invention to minimize unwindingproblems.

It is yet another object of the present invention to minimize sagsduring the unwinding of the plurality of elongated elements.

It is still another object of the present invention to avoid wrinkles inthe ultimate product.

According to a first aspect of the present invention there is provided aspool filled with two or more elongated elements wound in parallel andin several windings upon the spool. The distance between two neighboringelongated elements, as measured along a line parallel to the axis of thespool, is not more than 10 mm, preferably not more than 8 mm, e.g. notmore than 5 mm, along 90% of the length of each elongated element.

Indeed the inventors have experienced that the distance between theneighboring elongated elements wound on the spool is a criticalparameter. It does not only suffice to wind the elongated elements undersubstantially equal tensions and to wind the elongated elements withsubstantially equal lengths upon the spool, the elongated elements havealso to be wound as close as possible to each other without becomingentangled. As will be explained hereinafter, the greater the distancebetween two neighboring elongated elements, the greater the danger fortension differences in the unwinding elongated elements—even if theelongated elements have been wound under equal tensions and with equallengths. The greater the tension differences in the unwinding elongatedelements the greater the danger for sags in one or more of the elongatedelements and the greater the danger for wrinkles in the ultimateproduct.

The elongated elements may be steel elements such as steel wires orsteel cords.

In a particular embodiment of the invention, there is provided a spoolwherein one of the steel cords comprises steel filaments, a majority ofwhich is twisted in a first twist direction, and wherein another of thesteel cords also comprises steel filaments, a majority of which istwisted in a second twist direction. The second twist direction isopposite to the first twist direction.

Preferably the spool comprises two steel cords wound upon the spool. Onesteel cord is mainly twisted in an S-direction and the other steel cordis mainly twisted in a Z-direction.

According to a second aspect of the present invention, there is provideda method of minimizing sags when unwinding multiple elongated elementsfrom one single spool. The method comprises the following steps:

-   -   a) providing a spool;    -   b) winding multiple elongated elements in parallel and in        several windings upon the spool so that that the distance        between two neighboring elongated elements, as measured along a        line parallel to the axis of the spool, is not more than 10 mm        along 90% of the length of each elongated element.

In a preferable embodiment of the method the multiple elongated elementsare guided on a common pulley just upstream the spool in order to reduceas much as possible the distance s between two neighboring elongatedelements on the spool. The common pulley is located as close as possibleto the spool.

Most preferably the multiple elongated elements are kept separate fromeach other upstream the common pulley in order to avoid that theelongated elements would entangle with each other.

The common pulley preferably has a flat groove and most preferably thewidth of this groove is somewhat greater than the sum of the diametersof the multiple elongated elements. This gives the best results withrespect to minimizing the distance s while still avoiding theentanglement between two neighboring elongated elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described into more detail with reference tothe accompanying drawings wherein

FIG. 1 shows a spool according to a first embodiment of the presentinvention;

FIG. 2 shows a spool according to a second and particular embodiment ofthe present invention;

FIG. 3 gives a schematic drawing explaining the working of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a spool 10 according to a first embodiment of the firstaspect of the present invention. The spool 10 is provided with twoflanges 12′ and 12″. Two steel cords 14 and 16, both twisted inS-direction, are wound in parallel and adjacent to each other on spool10. The distance s, as measured along a line parallel to the axis 18 ofspool 10, is less than 5 mm.

FIG. 2 shows a spool 10 according to a particular and second embodimentof the first aspect of the present invention. The spool 10 is providedwith two flanges 12′ and 12″. A steel cord 14, twisted in S-direction,and a steel cord 20, twisted in Z-direction, are wound in parallel andadjacent to each other on spool 10. The distance s, as measured along aline parallel to the axis 18 of spool 10, is less than 5 mm. When usingspools according to this particular embodiment of the invention on acreel in the field of rubber tires, an S-cord and a Z-cord will lie, oneadjacent to the other in a composite ply rubber-steel cord. If all thespools on the creel will be spools according to the invention, therewill be an equal number of S-cords and Z-cords on average over the wholecomposite rubber-steel cord ply. S-cords will alternate on average withZ-cords over the whole composite ply. In such a configuration it islikely that any residual torsions present on S-cords may compensate onaverage any residual torsions present on Z-cords so that eventually cutcomposite strips rubber-steel cord do not exhibit curling. Within thecontext of the present invention, the terms “residual torsions” aredefined as follows: if one end of a specified length of cord is allowedto turn freely, the number of residual torsions is equal to the numberof revolutions counted. An imbalance of residual torsions over thetotality of steel cords within one composite strip rubber-steel cord isknown as the main cause of curling. Avoiding this imbalance reduces therisk for curling. And, as explained above, avoidance of curling mayfacilitate the automated handling of the strips. In such configurationit is sufficient that the steel cords present in the cut strips have onaverage no residual torsions. As a result it is no longer required tofine-tune the amount of residual torsions present on each single steelcord during its twisting step. This may considerably reduce theauxiliary equipment required, more particularly, the automatic torsioncontrol may be cancelled.

FIG. 3 explains the basic working of the present invention. Spool 10 isfilled with two steel cords 14, 16. There is a distance s presentbetween the two steel cords 14 and 16, measured along a line parallel tothe axis 18 of the spool 10. The two steel cords 14, 16 are wound fromspool 10 and are guided through one single fixed hole 22. Steel cords14′ and 16′ show the situation at the left flange 12′ and steel cords14″ and 16″ show the situation at the right flange 12″.

For the sake of the current calculations, the distance s is supposed toremain constant during the unwinding process.

Also for the sake of calculations, the hole 22 is supposed to be at adistance of y=300 mm from the spool 10, and at x=0 mm from the extensionof right flange 12″.

The spool width b is equal to 153 mm.

It is further supposed that the steel cord is of a 2×0.30 type, so thatthe cross-section A is equal to 0.141372 mm².

l₁ is the length of the unwound cord 14′, l₂ the length of the unwoundcord 16′, l₃ the length of the unwound cord 14″ and l₄ the length of theunwound cord 16″.

With the above assumptions, at with a value of intercord distance sequal to 10 mm, we obtain following values for the various lengths l₁,l₂, l₃, and l₄:l ₁ ={square root}{square root over (y ² +(b−x) ² )}=3003,899 mml ₂ ={square root}{square root over (y ² +(b−x−s) ² )}=3003,406 mml ₃ ={square root}{square root over (y ² +(x−s) ² )}=3000,017 mml ₄ ={square root}{square root over (y ² +x ² )}=3000,000 mm

The difference of the length difference, i.e. the change in lengthdifference between the situation at the left flange 12′ and the lengthdifference at the right flange 12″ is:(l ₁ −l ₂)−(l ₃ −l ₄)=0,476067 mm

Such a change in length difference results in a change in tensiondifference of${{\Delta\quad\sigma} \approx \frac{\left( {1_{1} - 1_{2}} \right) - \left( {1_{3} - 1_{4}} \right)}{E*A*y}} = {4,4868\quad{Newton}}$

With an intercord distance s different from 0 mm, the length differencebetween the unwound steel cords 14 and 16 changes continuously duringthe unwinding operation, which results in changing tension differencesin the unwound steel cords 14 and 16.

This change in tension difference is dependent upon the distance s andincreases as the distance s increases, as may be derived from thefollowing table. TABLE tension difference in function of distance s s[mm] Δσ (Newton) 0 0 0.5 0.239236 1 0.476904 1.5 0.713005 2 0.947537 2.51.180502 3 1.411899 3.5 1.641728 4 1.86999 4.5 2.096683 5 2.321809 5.52.545366 6 2.767356 6.5 2.987777 7 3.206631 7.5 3.423917 8 3.639634 8.53.853784 9 4.066365 9.5 4.277379 10 4.486824 10.5 4.694701 11 4.901

Dependent upon the unwinding tension applied to the spool, which mayvary from 400 gram (=3.924 Newton) to 3 kg (=29.43 Newton), considerablesags up to 0.5 m and higher may be registered. Sags occur each time thetension in one elongated element becomes zero. More exactly, when thedifference between the unwinding tension applied to the spool (this isthe sum of the unwinding tensions of the individual elongated elements)and the tension difference between the individual elongated elementsbecomes smaller than zero, one of the elongated elements will form asag.

The above simulation and calculation shows that it is important to keepthe distance s between the neighboring elongated elements as small aspossible.

The underlying layer consisting of the same type of elongated elements,the underlying layer is rough. So it is not always possible to keep thedistance s constant during winding. Nevertheless measures should betaken to keep the distance between the neighboring elongated elements assmall as possible.

1. A spool filled with two or more elongated elements wound in paralleland in several windings upon said spool, characterized in that thedistance between two neighboring elongated elements, as measured along aline parallel to the axis of the spool, is not more than 10 mm along 90%of the length of each elongated element.
 2. A spool according to claim 1wherein said distance is smaller than 5 mm.
 3. A spool according toclaim 1 wherein said elongated elements are steel elements.
 4. A spoolaccording to claim 3 wherein said steel elements are steel wires.
 5. Aspool according to claim 3 wherein said steel elements are steel cords.6. A spool according to claim 5 wherein one of said steel cordscomprises steel filaments, a majority of which being twisted in a firsttwist direction, and wherein another of said steel cords comprises steelfilaments, a majority of which being twisted in a second twistdirection, said second twist direction being opposite to said firsttwist direction.
 7. A method of minimizing sags when unwinding multipleelongated elements from one single spool, said method comprising thefollowing steps: a) providing a spool; b) winding multiple elongatedelements in parallel and in several windings upon said spool so thatthat the distance between two neighboring elongated elements, asmeasured along a line parallel to the axis of the spool, is not morethan 10 mm along 90% of the length of each elongated element.
 8. Amethod according to claim 7 wherein said method further comprises thefollowing step: guiding the multiple elongated elements on a commonpulley upstream the spool.
 9. A method according to claim 8 wherein saidmethod further comprises the following step: keeping the multipleelongated elements separate from each other upstream said common pulley.10. A method according to claim 9 wherein said common pulley has a flatgroove.
 11. A method according to claim 10 wherein said flat groove hasa width being greater than the sum of the diameters of the multipleelongated elements.